The present invention relates to instruments for analyzing a sample to determine its identity and constituents; and more particularly to such instruments which excite the sample in a glow discharge apparatus for subsequent analysis by a mass spectrometer or an optical spectrometer.
In many industrial and environmental situations, it is desirable to analyze a sample of a substance to determine the presence and relative concentrations of the constituent materials in the substance. A common apparatus for performing such analysis is a mass spectrometer which involves bombarding the sample in the gas phase with a beam of medium-energy electrons in a high vacuum. Typically an electron gun is utilized as a source of bombarding electrons. The mass of charged particles and fragments produced by that bombardment then is determined, as described by J. D. Roberts et al., Organic Chemistry methane to macromolecules, pp. 158-159, 1971, W. A. Benjamin, Inc.
Another type of spectrometry involves exciting the sample so that it emits light in the ultra violet, visible and/or infrared wavelengths. By analyzing the specific wavelengths emitted by the sample, a determination of the constituents can be made. Several techniques have been utilized for exciting materials including combustion and introduction into a glow discharge chamber where the sample in the gas phase is exposed to an electric discharge. Unfortunately, that excitation often destroyed the sample which in many instances is undesirable.
Present industrial and environmental issues often require analytical techniques with very high sensitivity and wide applicability. Detection of trace levels at or below part-per-million (ppm) levels are routinely required in many regulatory analysis. In certain cases, such as detection of PCB's, analytical techniques capable of distinguishing between harmful and harmless homologs are not available. Thus it is desirable to analyze constituents of a material based on negative ion formation via electron attachment to electronically excited molecules which has a very high efficiency and also is expected to occur in the vast majority of chemicals. In addition, information is desirable on the formation of positive ions and about emission characteristics of the given sample. An instrument which can provide all of this information would be particularly useful.